System and method for determining anisotropy of light-transmitting sheet specimen

Abstract

A system and method for determining the anisotropy of a sample of a light transmitting sheet is disclosed. The surface of the sample is irradiated with a polarized light which is directed through the sample to an analyzer element. The polarizing plane of the analyzer is matched to, or maintained in a predetermined angular relation to, the polarizing plane of the polarized light. The sample is rotated relative to the analyzer element so that the optical anisotropy can be determined from the relationship between the rotation angle and the output of measured light.

What we claim is: 
     
       1. A method for determining the optical anisotropy of a light transmitting sheet comprising the steps of: irradiating the surface of a sample of a light-transmitting sheet with a polarized light perpendicular to the surface;   directing the light transmitted through said sample to an analyzer element with the polarizing plane of the analyzer element being matched to, or maintained in a predetermined angle relative to, the polarizing plane of said irradiated polarized light, while adjusting the angle of relative rotation between said sample and said analyzer element polarizing plane;   directing the analyzed light from said analyer element to a light sensor unit to generate electric signals corresponding to the light intensity detected while adjusting sais angle of relative rotation; and   determining the optical anisotropy of said sample in accordance with the relation between the data of electric signals and said angle of relative rotation.   
     
     
       2. The method of claim 1 wherein the step of determining the optical anisotropy of said sample includes calculating the difference between the refractive indices of the polarized light in first and second directions in the sample plane. 
     
     
       3. The method of claim 1 wherein the polarized light irradiating the sample is laser light. 
     
     
       4. The method of claim 1 wherein the step of determining the optical anistropy of said sample includes calculating α, β and cos δ by solving the equations:   for θ=0, A.sup.2 p=β.sup.2 A.sup.2       for θ=π/2, A.sup.2 p=α.sup.2 A.sup.2       for θ=π/4, A.sup.2 p=[1/4(α.sup.2 +β.sup.2)1/2αβ cos δ]A.sup.2     where:   α=the amplitude transmission factor of polarized light in an x direction.   β=the amplitude transmission factor of polarized light in a y direction.   A=amplitude of incident light   θ=angle of incidence of linearly polarized light   δ=phase difference between velocity of polarized light transmitted in x and y directions   A 2  p=measured intensity of transmitted polarized light   
     
     
       5. The method of claim 4 wherein α 2  =β 2 . 
     
     
       6. The method of claim 4 wherein (β/α) 2  =0.7. 
     
     
       7. The method of claim 4 wherein said analyzer element has a polarizing plane perpendicular to the polarizing plane of said irradiated polarized light. 
     
     
       8. The method of claim 4 further comprising the step of determining the difference (n1-n2) between the indices of refraction in mutually perpendicular x and y directions in said sample plane according to the equation ##EQU3## where: λ=light wavelength d=sample sheet thickness   n1=sample sheet refractive index in x direction   n2=sample sheet refractive index in y direction.   
     
     
       9. The method of claim 8 further comprising the step of displaying the ratio α:β and the difference (n1-n2). 
     
     
       10. The method of claim 1 wherein said determining step further includes determining the orientation of said sample having a substantially constant thickness of taking the ratio TI (Vmin/Vmax)   where V is the light intensity measured through said analyzer element, said analyzer element polarization plane matching the polarizing plane of said irradiated polarized light.   
     
     
       11. A system for determining the optical anisotropy of a light transmitting sheet comprising: polarized light source means;   a sample of a light transmitting sheet positioned to be perpendicularly irradiated with polarized light from said light source;   means for analyzing the light transmitted through said sample and emitted from the surface of said sample opposite to the irradiated surface, said analyzing means having a polarizing plane matched to, or maintained in predetermined angular relation to, the polarizing plane of the polarized light from said light source means;   means for supporting said sample and said analyzing means, and for adjusting the relative rotation between said sample and said analyzing means with the polarizing plane of said analyzing means being matched to, or maintained in predetermined angular relation to, the polarizing plane of the light from said light source means;   angular sensing means for establishing a reference angular position for said relative rotation;   means for controllably driving said suporting and rotation adjusting means to cause said relative rotation within a predetermined angular range from said reference angular position;   light sensing means for detecting the light transmitted through said analyzing means to generate electric signals corresponding to the light intensity during said relative rotation;   a central processing unit for referencing the state of said angular sensing means to control said driving means, and for receiving said electric signals to determine the optical anisotropy of the sample from the relation between the data of said electric signals and the angular positions in said relative rotation; and   an output device for displaying or outputting the determined optical anistropy of the sample.   
     
     
       12. The system of claim 11 wherein said supporting and rotation adjusting means rotates said sample relative to said analyzing means, said analyzing means being held in a fixed position. 
     
     
       13. The system of claim 11 wherein said central processing unit determines the optical anistropy of the sample by calculating α, β and cos δ through solving the equations: ##EQU4## where: α=the amplitude transmission factor of polarized light in an x direction β=the amplitude transmission factor of polarized light in a y direction   A=amplitude of incident light.   θ=angle of incidence of linearly polarized light   δ=phase difference between velocity of polarized light transmitted to x and y directions   A 2  p=measured intensity of transmitted polarized light.   
     
     
       14. The system of claim 13 wherein said analyzer element has a polarizing plane perpendicular to the polarizing plane of said irradiated polarized light. 
     
     
       15. The system of claim 13 wherein said central processing unit further determines the difference (n1-n2) between the indices of refraction in mutually perpendicular x and y directions in said sample plane according to the equation: ##EQU5## where: λ=light wavelength d=sample sheet thickness   n1=sample sheet refractive index in x direction   n2=sample sheet refractive index in y direction.